Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 221912
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
212 PM CDT Sun Apr 22 2018

.SHORT TERM...
214 AM CDT

Through tonight...

High pressure is centered over the eastern Great Lakes this
morning with ridging extending back into the Upper Midwest. An
upper low is over the Great Plains and will shift east across the
lower Mississippi Valley tonight. Precipitation is expected
across downstate Illinois on the northern periphery of the system,
but should be dry in the local CWA through tonight. Clouds are
expected to clear from the north as the upper low digs farther
south today, which should help temps achieve a few more degrees
today in many locations. Expect afternoon highs in the mid 50s to
low 60s away from Lake Michigan. An increasing easterly gradient
will keep areas near the shores of Lake Michigan much cooler in
the 40s. Clouds may begin to increase again tonight as the low
lifts towards the Tennessee Valley. Expect overnight lows in the
mid 30s to low 40s.

Deubelbeiss

&&

.LONG TERM...
212 PM CDT

Monday night through Sunday...

Closed upper low is progged to be over the lower Tennessee Valley
Monday evening, eventually opening up and lifting out to the
northeast through the Ohio Valley Tuesday and Tuesday night as it
gets "kicked" by northern stream short wave trough digging across
the northern/western Great Lakes region. Vort energy wrapping
northward around the main mid-level circulation spreads mid-level
moisture into the dilatation axis over the area Monday night into
Tuesday, with a corresponding potential for some light rain across
the southeast half of the forecast area, especially along/east of
I-55. Pops peak Monday night, then gradually diminish from the
west during the day Tuesday as the system pulls slowly off to the
east. The northern stream "kicker" digs across the Lakes into
Tuesday night, with a cold front pushing across the area and
enhancing blustery north-northeast winds by Wednesday morning.

Surface high pressure then builds across the area Wednesday into
Wednesday night, with dry but cooler weather on persistent but
slowly diminishing north-northeast winds. After seasonable temps
around 60 Tuesday (though a little cooler in thicker cloud cover
and light rain southeast), cooler air mass looks to keep temps in
the 50`s in most area, and only in the 40`s near Lake Michigan.
Lighter winds and mainly clear skies within the ridge axis
Wednesday night will allow for favorable radiational cooling
conditions, with min temps falling into the mid-30`s for the most
part by sunrise Thursday.

Medium-range guidance digs another upper trough across the region
Thursday night into Friday, though shows considerable spread in
developing another closed upper low somewhere from the southern
Great Lakes to the lower Mississippi Valley. Given the model
differences with the details of this evolution, timing of the cold
front and associated precip chances are also a bit out of sync,
but appear at this time to be focused later Thursday or Thursday
night, with a slight warm-up Thursday ahead of the front. Slower
ECMWF and Canadian solutions would likely result in pops lingering
into early Friday as well. Upper trough then moves off to the
east of the area, though global guidance hints at another
disturbance moving through northwest flow aloft Saturday, which
trails a cold front into the forecast area Saturday night or early
Sunday. It does look like warming aloft would support milder
temps next weekend, likely well into the 60`s, though the location
of the cold front will determine the details of that, as winds
could be off the lake across the Chicago area at that time.

Ratzer

&&

.AVIATION...
For the 18Z TAFs...

VFR conditions will continue through the period. East northeast
winds have increased slightly today, with some gusts now likely
through the afternoon. Expect an east/northeast wind to persist
tonight into Monday.

Rodriguez

&&

.MARINE...
124 AM CDT

Conditions continue fairly quiet over the lake through early
Tuesday. Northeast winds today and Monday will be stronger (10-20
kt) than recent days across the southern third of the lake. A
cold front will push down the lake on Tuesday night, turning winds
northerly with a sharp increase in speed. Small Craft Advisory
conditions are presently forecast all of Wednesday for the
Illinois and Indiana nearshores. Model solutions then largely
spread beyond that, with a blended solution of low pressure
dropping southeast over the Great Lakes late in the week.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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